Defect assessment of optical surfaces using the light scatter sensor HOROS

Light scatter measurement and analysis are widely used for the characterization of micro and nano structures as well as defects on optical surfaces. In particular the 3D Angle Resolved Scattering (ARS) of particles, digs, and scratches provides characteristic features usable for defect classification. The recently presented light scatter sensor horos (high sensitive optical roughness sensor) constitutes an elaborated tool for 3D-ARS measurements of various light scattering phenomena as will be demonstrated by roughness and defect characterization over the entire surface area. The compact and fast CMOS-matrix based measurement concept enables easy combination with independent characterization techniques like white light interferometry. Based on this combination a direct comparison of ARS features and defect geometries as well as an investigation of their correlation becomes possible. In addition, the application of light scatter modeling to determine defect size and shape from the ARS distributions is investigated.